Recently having come into general use is a communication system for enabling a teleconference over a communication network such as the Internet, because of a demand for cutting a traveling cost and traveling time. When such a communication system is used, a teleconference can be held by allowing image data and audio data to be exchanged among a plurality of communication terminals (see Japanese Patent Application Laid-open No. 2008-227577).
In addition, disclosed is a video phone system providing one communication terminal with two different communication functions using different communication protocols, e.g., the personal digital cellular (PDC) protocol and the personal handy phone system (PHS), respectively, and communication is established while switching these two different communication protocols (see Japanese Patent Application Laid-open No. 2001-326972).
In these conventional two communication protocols, a signaling protocol for connecting to and disconnecting from a destination and an encoding protocol for encoding call data are both different. In other words, such a conventional communication terminal is a single housing merely provided with two different communication functions using completely different communication protocols, and causing one of the functions to operate exclusively. Therefore, it has been impossible for a plurality of communication functions using the same signaling protocol but different encoding protocols to be used on the same terminal.